# Subnet creation exceeding number of hosts [duplicate]

I have a question, and I have some confusion.

I have to create subnets for six different teams. All IP addresses should start with 172.168.1.x only.

Team 1 -> 5 Hosts
Team 2 -> 16 Hosts
Team 3 -> 13 Hosts
Team 4 -> 37 Hosts
Team 5 -> 65 Hosts
Team 6 -> 12 Hosts


It looks like it is not possible. I think I have to reduce the host count from some team.

Can anyone can help?

• Classful networking is dead. And even with the old definition of Classful an address starting with 178 can never ever be a Class C address. – Jens Link Mar 26 '16 at 8:31

In other words you have a /24 network that you want to divide in 6 networks.

Let's reorder the teams by size:

Team 5 : 65 hosts
Team 4 : 32 hosts
Team 2 : 16 hosts
Team 3 : 13 hosts
Team 6 : 12 hosts
Team 1 : 5 hosts


and compare them with subnet sizes:

Similarly:

/25 : 125 hosts
/26 :  61 hosts
/27 :  29 hosts
/28 :  13 hosts
/29 :   5 hosts


So we see that we need at a minimum:

Team 5 : 65 hosts -> /25
Team 4 : 32 hosts -> /26
Team 2 : 16 hosts -> /27
Team 3 : 13 hosts -> /28
Team 6 : 12 hosts -> /28
Team 1 :  5 hosts -> /29


## Can we divide a /24 network to fit all those networks in ?

A way to look at it would be:

• Divide the /24 in two /25 networks.
The first /25 is assigned to Team5, the second /25 is further sub-netted.

• Divide the second /25 in two /26 networks.
The first /26 is assigned to Team4, the second is further sub-netted.

• Divide the second /26 in two /27 networks.
The first /27 is assigned to Team2, the second is further sub-netted.

• Divide the second /27 in two /28 networks.
the two /28 are assigned to Team3 and Team6.

Nothing left for Team1... ...too bad.

You could for example:

• Group Team 1 with another team (so both team will use the same network).
• User for another team 2 networks, i.e.:
Separate the the first /25 that was assigned to Team 5 in two /26 networks.
Assign the first one to the first 63 hosts of Team5.
Subnet the second one in four /28 networks
Assign the first /28 to the other members of Team 5, the second one to team 1 and you have two /28 available.
• great.. clearly explained, one more quick question, what means writing the above in CIDR notation? – karthikeayan Mar 26 '16 at 9:04